In compressed-air brake systems of wheeled vehicles, such as motor vehicles and rail vehicles, valve units of the above-mentioned type may be used as brake valves, as relay valves, and as ABS control valves. Such a valve unit has an inlet valve and an outlet valve. Via the inlet valve, a brake pressure output, to which a brake circuit or a brake line leading to a wheel brake cylinder can be connected, can be alternately connected to or shut off from a brake pressure input, to which a brake line coming from a brake valve or relay valve can be connected. Via the outlet valve, the brake pressure output can be alternately connected to or shut off from a vent output which normally leads via a silencer to the environment.
Because of the large volume flows to be switched and correspondingly large flow cross-sections to be opened and closed, the inlet valve and outlet valve are often configured as pneumatically actuatable diaphragm valves, which can be controlled via a respective pilot valve configured as a 3/2-way solenoid valve. A diaphragm valve has a largely circular, disk-like, flexible diaphragm which at its edge is clamped in the valve housing, usually via a ring bead placed in a housing-side ring groove and oriented axially on the pilot valve side, i.e. axially facing the housing part containing the pilot valves.
On the axial inner side of the diaphragm on which the flow channels connected to the compressed air inputs and outputs are arranged, and coaxially to the actuation axis of the respective diaphragm valve, a cylindrical central channel with a circular valve seat facing the diaphragm and an outer ring channel concentric thereto are arranged. On the axially opposite outer side of the diaphragm, a control chamber is arranged which can be pressurized by the assigned pilot valve alternately with a high control pressure normally taken from the brake pressure input, or with a low control pressure, normally corresponding to ambient pressure, taken from the vent output or another point.
When the control chamber is pressurized with the high control pressure, the diaphragm is pressed against the valve seat, whereby the central channel is shut off from the outer ring channel, which corresponds to the closed state of the diaphragm valve concerned. When the control chamber is pressurized with the low control pressure, the diaphragm, which lies automatically on the valve seat due to its shaping and/or a valve spring, is raised from the valve seat by the brake pressure prevailing in the flow channels and displaced in the direction towards the control chamber, whereby the central channel is connected to the ring channel, which corresponds to the open state of the diaphragm valve concerned.
With regard to the geometric arrangement of the compressed air inputs and outputs of the inlet and outlet valves formed as diaphragm valves, and the pilot valves formed as solenoid valves, in a valve housing, valve units are known in which the compressed air inputs and compressed air outputs and diaphragm valves are arranged with parallel actuation axes in a first housing part, while the pilot valves are arranged in a second housing part, and in which the diaphragms of the diaphragm valves are each clamped between two housing parts via a respective ring bead placed in a housing-side ring groove and axially facing the housing part containing the pilot valves.
Such a valve unit is described for example in U.S. Pat. No. 3,977,734 A. In this known valve unit, a valve housing is divided into a lower housing part and an upper housing part via a separating plane which is horizontal in the installation position. The brake pressure input, the brake pressure output and the vent output are arranged in the lower housing part. The pilot valves are arranged in the upper housing part with mutually parallel actuation axes oriented perpendicularly to the separating plane. The diaphragm valves are arranged in the lower housing part with parallel actuation axes, wherein the diaphragms are clamped between the lower housing part and the upper housing part in a common diaphragm plane largely corresponding to the separating plane.
In a further such valve unit known from EP 0 498 584 B1, the valve housing is divided into an input housing and an output housing with a separating plane which is vertical in the installation position. The brake pressure input is indeed arranged in the input housing, but connected directly via a connecting channel to an input channel located in the output housing. The brake pressure output and the vent output are arranged directly in the output housing. The pilot valves with parallel actuation axes are combined in a valve block which is inserted in sealed fashion in a recess of the input housing. The diaphragm valves with parallel actuation axes are arranged in the output housing, wherein the diaphragms are clamped between the input housing and the output housing in a common diaphragm plane largely corresponding to the separating plane.
Finally, U.S. Pat. No. 8,672,421 B2 describes a valve unit in which a valve housing is divided into a lower housing part, an upper housing part and an intermediate plate arranged in between, with separating planes which are largely horizontal in the installation position. The brake pressure input, the brake pressure output and the vent output are arranged in the lower housing part. The pilot valves are arranged in the upper housing part with mutually parallel actuation axes oriented perpendicularly to the separating plane between the intermediate plate and the housing upper part, and with the same actuation direction, wherein the valve seats are part of the intermediate plate. The diaphragm valves with parallel actuation axes are arranged in the lower housing part, wherein the diaphragms are clamped between the lower housing part and the intermediate plate in a common diaphragm plane largely corresponding to the separating plane between the lower housing part and the intermediate plate.
The ring beads of the diaphragms usually have a slight oversize in relation to the ring grooves which are stationary relative to the housing, in order to guarantee a mechanically stable and pressure-tight clamping of the diaphragms between the respective housing parts. Due to this clamping, however, the bead material of the diaphragms consisting of an elastomer plastic is necessarily displaced radially inwardly out of the ring groove, which leads to local thickening and bulging of the diaphragms. As well as possible function disruption, these usually irregular deformations may also lead to tearing of the diaphragms and hence to premature failure of the diaphragm valves.